Lovers in a Dangerous Spacetime, a thrilling 1- to 4-player couch co-op adventure.

It is an absolutely cute adventure that you can embark on at home with anyone to protect, defend and confront the many dangers in this game's fictional space plus, to show your love for supporting creativity and risk taking by independent developers.

-Caribbean Fever-

For the anniversary party, I would recommend ‘Lego Batman: The Video Game’, to celebrate 13 years of DRM-free games on GOG. The game was released on 29 September 2008, a short while after GOG was launched by CD Projekt Red.

Sacred 1, Sacred 2 or Dungeon Siege - the co-op games that filled the void when Diablo 2 finally started to lose its luster. Really enjoyed the times spent with each of them.

In a perfect world I'd love to play a game of Ebonstar (an Amiga game from 1988). My friends and I would bang on that old Amiga keyboard until my father lost his mind.

I have fond memories of playing Tie Fighter with my buddy. One of us used the joystick, while the other one controlled shields and energy over the keyboard. I miss those days.

So true. I remember doing this with my friends as well!

The thing about co-op games is that they generally need to be short because you won't be able to always have someone available to be player 2. With that said, the recommendations for cRPGs are fair if you can find someone willing to spend >50 hours doing co-op. I often find that hard to come by, so my favorites in group settings tend to be more about making short experiences that intrigues everyone for a story-based ending.

I would argue that traditionally single player games like the Tell-Tale's Walking Dead series or Wolf Among Us actually are fun when played Cooperatively in a group setting. You make all of the choices together and watch the outcome. Games like Monster Prom are also great for this!

IT's got to be Warcraft 2, LAN 3v3 COOP!

My greatest memory of Warcraft 2 LAN COOP goes way back to the late 90's. Imagine being invited over to your friend's apartment for a LAN party, where everyone brings their big...giant...desktop PC, which of course includes monitor/keyboard/mouse. Once arriving you form two 3 player teams and separate into two rooms, one of which is a bedroom that has been cleared of the bed so a big table could be set up. After taking 30 minutes or so to set up and get connected, you move on to discuss strategy for another 15 minutes or so. Finally its time to duke it out! As anyone that's played 3v3 can tell you, this game is about resource gathering skirmishes until sufficient forces have been built up to start attacking your enemy. I recall my greatest game lasting 3+ hours, with literally no resources left to gather, 2 players on each side left, and very few forces on each side. The last hour or so was a cat and mouse game where each side would throw a distracting force at one player to attempt to draw all enemy forces there while the other player would attack the other players base. Eventually the team I was playing against managed to wipe out the base of one of our remaining players and we conceeded. What made this game so fun though, was the fact that even though I was the first player eliminated, I was on my feet for the next two hours helping the players coordinate and offer suggestions on strategy. What other COOP game can keep a player so engaged for almost two hours after being eliminated!

Rocky & Pocky

You win :)

I recommend Mechwarrior 5: Mercenaries with the two newest DLC's. That would be awesome to play co-op.

Worms Ultimate Mayhem FTW!!!
Still remember back in the day having LAN parties with my mates and this was the game that always landed up taking most of our time (even with multiple other releases available at the time). Great fun!

We Were Here

Puzzle co-op, voice communication. Nothing groundbreaking but fun for a few hours. Not to mention, it's a series so if you like one and want more then you get just that. Plus, the first one costs nothing. Just a shame the series isn't here on GOG, though with the lobby system I kinda see why.

Hands down the best coop game from the past few yours is Divinity: Original Sin II.

Altough from the earlier generations me and the boys had countless sleepless night playing couch-coop Crash Bash and LotR: Return of the King on the PlayStation 1 and PlayStation 2.

I'll throw in a unorthodox recommendation. System Shock 2.

As good as the single player is, the co-op mode is notoriously buggy and unstable. You'd probably need to play through the game in one sitting if you want to have any chance of completing it in this mode, as the save often breaks when you close the game. With that being said, I had a lot of fun when I played it with a couple of friends (there's support for up to four players!). Beer was involved too, and there were lots of great moments. We played over a couple of evenings, but we pretty much had to start a new game every time. At our best attempt we managed to complete half the game.